JPS6346792B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a storage material mainly composed of magnesium chloride hexahydrate. [Background of the Invention] Magnesium chloride hexahydrate (MgCl ₂ .6H ₂ O; melting point 117°C) is inexpensive and has a large latent heat, so it is a promising substance as a heat storage material for air conditioning or waste heat recovery. However, it causes a significant supercooling phenomenon during heat dissipation, and does not release latent heat even if the temperature drops by about 25 degrees Celsius below the freezing point. FIG. 1 shows the solidification characteristics of magnesium chloride hexahydrate, with time t plotted on the horizontal axis and temperature T plotted on the vertical axis. In this experiment, 100g of magnesium chloride hexahydrate was placed in a glass container, placed in an electric furnace at 150℃, completely melted, and then left to cool in the air at a temperature of approximately 25℃. For measurement, the hot junction of the thermocouple was placed in magnesium chloride hexahydrate in a glass container, and the thermoelectromotive force was measured by placing it in a dot type recorder. The temperature of magnesium chloride hexahydrate decreases over time, and supercooling stops at 90°C, after which it returns to its freezing point, Ts = 117°C, and begins to release latent heat. Freezing point Ts and supercooling recovery temperature Tr = 90
The difference in temperature is as much as 27°C, and the existence of this temperature difference has often caused difficulties in the thermal design of heat engines, refrigeration equipment, and heating equipment that use latent heat storage tanks.
For example, in a capsule heat storage tank that houses a large number of heat storage capsules (metals such as copper and stainless steel) containing a heat storage material (magnesium chloride hexahydrate), the temperature of the heat medium (oil, fluorocarbon, etc.) flowing outside the tank is 100°C.
Then, since the heat storage material does not release latent heat of solidification, the temperature must be lowered to at least 90°C or lower. If the temperature is extremely lowered in this way, it is inconvenient that the efficiency of a heat engine, refrigeration device, or heating device using a latent heat storage tank decreases. [Object of the Invention] An object of the present invention is to provide a heat storage material that suppresses the supercooling phenomenon of magnesium chloride hexahydrate described above. [Summary of the Invention] In order to achieve the above object, the present invention includes magnesium silicate (Mg ₂ SiO ₄ ) and magnesium silicate pentahydrate (Mg ₂ Si ₃ O ₈ ) as a nucleating agent in magnesium chloride hexahydrate. 5H ₂ O), sodium metasilicate pentahydrate (Na ₂ SiO ₃・5H ₂ O), sodium metasilicate 9
It contains one or more substances from the group consisting of aqueous salt (Na ₂ SiO ₃ .9H ₂ O) and sodium silicate (Na ₄ SiO ₄ ). [Embodiments of the Invention] Examples of the present invention will be described below. [Example 1] A mixture of 100 g of magnesium chloride and 0.01 g of magnesium silicate was placed in a glass container, and the container was placed in an electric furnace at 150°C to completely melt it. It was left to cool in the air. Supercooling stopped at 115℃, the freezing point returned to Ts = 117℃, and latent heat release started. In this experiment, the degree of supercooling ΔTs, that is, the freezing point Ts and the supercooling recovery temperature Tr
The difference was found to be as small as 2°C. The results are shown in FIG. After conducting the same experiment 20 times with the same sample, the degree of supercooling ΔTs was still 2.
It was about ℃. The latent heat of this heat storage material was measured using a differential calorimeter and was found to be 41kcal/Kg. Furthermore, when we conducted a similar experiment by changing magnesium silicate to magnesium silicate pentahydrate, the degree of supercooling was still 2°C.
I was able to find a trowel to hold it down. [Example 2] A mixture of 1 g of sodium metasilicate pentahydrate added to 100 g of magnesium chloride hexahydrate was placed in a glass container, and the same experiment as in Example 1 was conducted. As a result, it was found that the degree of supercooling ΔTs was 5°C. . When a similar experiment was conducted by replacing sodium metasilicate pentahydrate with sodium metasilicate nonahydrate, the degree of supercooling could still be kept at 5°C. [Example 3] A mixture of 100 g of magnesium chloride hexahydrate and 0.05 g of sodium silicate was placed in a glass container, and the same experiment as in Example 1 was conducted. As a result, it was found that the degree of supercooling ΔTs was 5°C.
As a result of measuring the latent heat of this heat storage material with a differential calorimeter,
It was 41kcal/Kg. The above results are summarized and shown in Table 1. From this table, if no nucleating agent is added (No.
It can be seen that the degree of supercooling ΔTs is significantly smaller than in 4).

[Table] Furthermore, when we conducted an experiment with the combined addition of nucleating agents, we found that the effect was even higher than when they were added alone. The results are shown in Table 2.

[Table] Furthermore, the heat storage material to which a nucleating agent is added in combination,
It was found that when glass fibers containing air bubbles were mixed, the degree of supercooling was reduced by about 50%. An example is shown in Table 2 No. 4. Glass fibers also help prevent two-phase separation. Glass fibers with air bubbles are made by cutting a long bundle of glass fibers with scissors. The amount of nucleating agent added may be extremely small;
As shown in Example 1, sufficient effects are produced even at 0.01 part by weight. There is no particular upper limit to the amount of nucleating agent added, but if too much is added, the heat storage capacity will decrease, so it is preferably 10 parts by weight or less. [Effects of the Invention] As explained above, according to the present invention, the degree of supercooling of magnesium chloride hexahydrate, which is a heat storage material, is significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the solidification characteristics of a conventional heat storage material, and FIG. 2 is a diagram showing the solidification characteristics of the heat storage material of the present invention shown in Example 1.

Claims (1)

[Claims] 1. Magnesium chloride hexahydrate, magnesium silicate, magnesium silicate pentahydrate as a nucleating agent,
A heat storage material containing one or more substances selected from the group consisting of sodium metasilicate pentahydrate, sodium metasilicate nonahydrate, and sodium silicate. 2. The heat storage material according to claim 1, which is made by adding 0.01 parts by weight to 10 parts by weight of a nucleating agent to magnesium chloride hexahydrate. 3. The heat storage material according to claim 1 or 2, which is formed by mixing glass fibers containing air bubbles.